other disease Mako shark

Fishing gear injuries and accidental bycatch of the shortfin mako shark

The shortfin mako shark (Isurus oxyrinchus) is one of the fastest shark species in the ocean, yet also one of the most affected by bycatch—the unintentional capture of an animal during fishing operations targeting a different species, such...

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Definition Signs Causes Diagnosis Treatment Prevention Complications When to see a vet Prognosis FAQ Sources Affected species

What is it?

These accidental captures occur mainly during longlining (long lines fitted with many hooks) or with gill nets or drift nets. The animal becomes trapped and injured, sometimes for several hours before being returned to the water or brought aboard.

This sheet describes the physical trauma that these fishing devices cause in the mako: lacerations, constriction by lines, injuries to fins and mouth, as well as the physiological consequences of capture stress. This is not a "disease" in the classical sense, but a collection of accidental human-caused lesions that are major for the conservation of the species.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Related signs — each one links to its page:

Non-healing wound Difficulty breathing Abnormal swimming Reduction Swelling Pain Paralysis

A shortfin mako shark that is a victim of accidental capture may present deep wounds around the mouth, gills, or skin, caused by hooks, lines, or mesh.

When the animal remains tangled in a net or line for an extended period, constriction is often observed: a deep circular mark, sometimes down to bone or cartilage, at the caudal peduncle (the base of the tail) or behind the pectoral fins. This constriction can lead to swelling of tissues downstream of the wound.

Hooks may remain embedded in the jaw, throat, or even be swallowed, causing internal injuries and difficulty feeding.

Intense stress from capture causes widespread muscle exhaustion, abnormal or disoriented swimming, difficulty breathing when the animal is immobilized out of water or at the surface, and sometimes temporary paralysis.

In the longer term, if the animal survives and is released, scars, fin deformities, or persistent difficulty swimming normally may remain.

When to consult without delay

This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.

Causes and risk factors

Trauma results directly from contact with fishing gear: longline hooks, trolling lines, gill nets, or drift nets. The mako, because of its speed and active behaviour, often struggles violently once captured, which aggravates injuries from friction and constriction.

Capture stress results from intense muscle effort combined sometimes with oxygen deprivation, particularly in this species which needs to swim continuously to move water over its gills.

The mako is particularly exposed because it shares the same zones and depths as tuna and swordfish, species targeted by pelagic longlining throughout the Mediterranean, Atlantic, and other oceans.

Its active behaviour and natural curiosity towards bait increase the risk of hook bites. Juveniles and pregnant females, often present in coastal nursery areas, may also be captured by coastal gill nets.

The soak time of the fishing gear (longlino left for several hours) and zones with high fishing effort density increase the probability and severity of trauma.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Assessment of a shortfin mako injured by fishing gear occurs mainly through direct observation during retrieval on deck or examination by marine biologists and veterinarians specialising in aquatic species, particularly within scientific monitoring or rescue programmes.

Examination covers wound depth and location, presence of a retained hook, any signs of constriction, gill colour, and the animal's swimming behaviour once returned to water if possible.

In a research or rescue context, tools such as satellite tagging allow tracking of post-release survival in injured individuals.

Treatment

No conventional medical treatment is applicable at sea. Management consists mainly of first aid measures undertaken by crew or scientific teams: careful removal of the hook when possible without worsening the wound, or cutting the line flush with the mouth if the hook cannot be removed safely.

In rare cases where care is provided at specialised facilities (aquariums, marine care centres), wound care and veterinary monitoring using aquatic antibiotics may be considered, but this remains exceptional for this pelagic species, which is difficult to maintain in captivity.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

Prevention relies primarily on fishery management measures: using circular hooks that reduce the risk of deep hooking, shortening soak times for longlines, and training crews in safe handling and rapid release of non-target sharks.

Temporary or spatial fishing closures in known shortfin mako nursery grounds, along with compliance with catch quotas and minimum size limits set by regional fishery management organisations, help limit bycatch impacts.

Educating fishermen on species identification and proper release practices—avoiding removing the animal from water, cutting the line close to the hook rather than tearing it out—reduces the severity of injuries.

Possible complications

Possible complications include secondary bacterial infection of wounds by marine bacteria, tissue necrosis from prolonged constriction, inability to feed normally if a hook remains lodged in the mouth or throat, and general weakness potentially leading to delayed death after release, even if the animal appeared initially viable.

Capture stress can also cause severe internal physiological imbalances, invisible to the naked eye, that compromise medium-term survival.

When to see a veterinarian

Presence of a hook or line still attached to the animal after capture.

Deep wound, visible constriction, or significant bleeding.

Abnormal swimming, disorientation, or lack of response after release.

Prolonged immobilisation out of water or at the surface before release.

Any accidental capture of shortfin mako must be reported to the competent authorities or fishery management organisations.

Prognosis

Prognosis depends heavily on how quickly the animal is returned to water and the severity of injuries. A shortfin mako released quickly with superficial wounds has good chances of survival.

Conversely, deep constriction, prolonged capture, or injury affecting the gills or internal organs significantly worsens the prognosis. Satellite tracking studies show that delayed mortality—the animal dying after release, sometimes several days later—is a frequent reality and difficult to quantify precisely for this species.

Frequently asked questions

Can an accidentally caught mako shark be saved?

Yes, if the capture is brief and the injuries are limited, a quick and careful release back into the water significantly improves its chances of survival.

Why is the mako so often a victim of bycatch?

It shares the same hunting grounds as tuna and swordfish, species targeted by longline fishing, which makes it particularly vulnerable to hooks and lines.

Should you remove the hook before releasing the animal?

It is recommended to cut the line as close as possible rather than forcing the hook out, which limits worsening the injury.

Is this species protected?

The shortfin mako shark is classified as a threatened species by several international organizations, and its capture is regulated by specific fishing regulations that vary by region.